Fiber composite material, particularly carbon-fiber-reinforced plastics and fiberglass reinforced plastics are used in many forms, particularly in the manufacture of aircrafts. Increasingly, such critical components as wings and center wing boxes are made of fiber composite materials.
The semi-finished product costs of the materials used are relatively high and a reduction of costs via the manufacturing process is difficult. This is mainly possible by reduction of material waste and rework. Additionally, high costs result from the manufacture of molds which are used for mass production of structural elements. Such molds are usually made of metallic materials by use of a suitable procedure such as cutting or milling. Thus, such molds are very precise, but also heavy, expensive and require a lot of effort.
Due to the accuracy of the tools the quality of a component can also be further improved by automation, e.g. combination and shortening of individual production steps. At the same time, this also leads to a reduction in production costs. In case of the available manufacturing processes the first step is the cutting of the fiber ply and following that there is the placing of the fiber ply onto the tool. Both steps can be performed manually or be automated, in this case the differences in investment costs for facilities and operation stay in contrast to the result achieved and manufacturability.
Additionally, especially in case of non-planar structures, but also due to the semi-finished material, a preforming is required. Either by application of a so-called binder, heat or vacuum or with a suitable combination thereof the flat semi-finished fiber is brought into the required form. Multiaxial ply which does not need to be remolded is not suitable for all geometries and also extremely expensive.
Following the preforming the mold is sealed or closed and it follows the curing, respectively resin injection in an autoclave. The utilization of a cold-curing resin system and non-use of the autoclave are possible but lead to a reduction in component quality.
The process of preforming is associated with great effort and additional costs. The use of a binder requires not only the material costs, but also application of heat which might be—depending on the components—required for any layer. When working with vacuum technology, in addition to the associated time expenditure there is also an increase in waste volume and there are also additional costs.
On the side of the molds there are high costs for the material itself but also for the production of the molds. The process is long-drawn-out and requires a lot of effort. Thus, in case of, in aviation typical, overall lengths of several meters it requires large-scale processing systems. Tools of this size are also very heavy and therefore difficult to handle.
The manufacture of a component is done in several steps, and the preforming and sealing require a lot of effort.
Additionally, metallic molds are inflexible. In case of a changing curvature of a structural element manufacture of a complete new mold is required. Especially, when during the development phase of a structure such parameters do change, considerable additional costs will result.
The described influencing factors lead—as a whole—to increased production costs for fiber composite parts, especially for small volume production and reduce the achievable production rates. Thus, the cost-effectiveness of the manufacturing process is adversely affected. Generally, changes in structure can not be considered later with the use of an unchangeable tool. Such changes might be, for example, elevations and depressions which are caused due to local changes in thickness of the support surface.